No one has mentioned:
You can use an 18v AC supply, and a couple of diodes, to give you the plus an minus voltage to drive the point.
You can use an 18v DC supply, no diodes and a DPDT switch, to switch the point.
Both the above need wiring back to supply, and switches.
You can use DCC (digital) to control the same point-motors. In this case, the power and control, can come from the track. - You have a decoder connected to the track, which takes commands from your handset/central-station, and then feeds the point-motor. You can get single decoders (which drive one point) or you can get one unit which will drive four points. The four point unit does need wiring from itself to each point-motor.
You can use air, as Jon said. - For this you need a small compressor, but this can be indoors, and you connect to the 'air-motor' with tubing similar to windscreen-washer tubing.
You can have a central control panel (the valves look like switches, from the front) and/or local controls out on the layout.
You can use 'wire in tube' from convenient points on the layout.
You can also use radio control: Usually to a central point on the layout, with wired connections to servo's to drive the points (signals too, if you want). -This 'central location' does require a source of power. Could be battery (possibly, solar-charged), could be derived from the track.
Limited commercial 'ready to go' product for this..
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